One of my favorite albums, following the style Self-Evident established on Endings; mind bending rhythms and harmonics captured in relatively straight-forward and familiar song structures. The level of craftsmanship is so high that you don't even notice the craftsmanship. Nothing seems forced.
I find Fortress slightly less groovy and heavy than Endings, but it has more memorable, intricate passages.
Along with Endings this is quite possibly the best math-rock on the planet.